This invention relates to a video display processor for desktop computers processing multi-media signals.
Computer multi-media signal processing involves combining and manipulating graphical and video images, the video images involving high data rates, particularly for moving images. Such systems are typically required to convert signals of the form received from a TV station, usually in a YVU or YCrCb color model, to RBG, the form usually used by a computer display, or vice versa, while adjusting brightness and correcting for color. They are required to perform blends, and scale the signals (stretch and/or contract) for the display, so that for example different sized video images can be superimposed in separate different sized windows. The typical host CPU of a computer system is hard-pressed to service these requirements in real time, and at the same time maintain service to other computer peripherals and devices.
For example, graphical stretches and reductions previously tended to be software implementations, and were application specific. However these are unsuitable for stretching or reducing live video images, due to the intensity of use of the computer CPU, creating a large overhead. In order to minimize CPU overhead, hardware scalers were produced. However these were typically used in digital to analog converters which translate the output of the graphics or display circuit immediately previous to the display. These scalers have only been able to scale upwards to multiples of the image source size. Further, since the output of the scaler is an analog signal suitable for the display, the image signals could only be displayed, and could not be read back digitally or operated on again.
Display processors for desktop computers were in the past able to superimpose one object upon another, for example the display of a cursor over background graphics. Such a processor typically incorporates a destination register, which stores pixel data relating to pixels to be displayed. Such data is often referred to as destination data. Other pixel data, to be superimposed (i.e. mixed) over the destination data, is stored in a source register and is referred to source data. A computer program controls software comparisons of the pixel values, and selects for display the pixel value having either a component or a value which is in excess of the corresponding value of the destination pixel.
While such an operation has been successful for graphical data, even graphical data with a varying component, such as data which varies due to a moving cursor, it has not been very successful to provide a rich array of capabilities when video data is to be mixed with video data or with graphics data. Yet these capabilities have become increasingly important as multimedia demands are made on the desktop computer. One of the primary reasons for the inability to provide such capabilities is that with software comparisons, excessive interrupt and processing demands are made on the central processor, which inhibits it from servicing the remainder of the computer in a timely fashion.
A description of software processing of pixel data, including mixing of graphical data, may be found in the text xe2x80x9cGraphics Programming For the 8514/Axe2x80x9d, by Jake Richter and Bud Smith, MandT Publishing, Inc., Redwood City, Calif., copyright 1990, and which is incorporated herein by reference.
In order to solve this problem, a separate graphics processor system has been designed, containing a video sub-system. Except for the loading of a video memory which interfaces the video subsystem, the present invention operates independently of the host CPU, thus greatly relieving it of major operational overhead. It can thus service the remainder of the system, increasing its response time. Yet full motion processed multi-media signals can be provided on a computer using the present video subsystem invention.
In accordance with the present invention a video display processor is comprised of apparatus for receiving digital input signal components of a signal to be displayed, apparatus for converting the components to a desired format, apparatus for scaling and blending the signals in the desired format, apparatus for outputting the scaled and blended signals for display or further processing and an arbiter and local timing apparatus for controlling all of the apparatus substantially independently of a host CPU.